The present invention relates to a light transmitting tube to be employed for illuminations, projectors, and the like and, more particularly, to light transmitting tube to be suitably employed in case that the tube is used in an environment where the tube is bent to have a small radius or is bent at many portions, or in case that a flexible tube surrounding an optical transmission tube has a small inner diameter.
A neon tube and a fluorescent tube have been used as a light emitting member for providing light in length of several meters. However, the neon tube and the fluorescent tube require high voltage. The neon tube or the fluorescent tube can not be used in water or at a place to be wet with rain or snow because dangers including electric shock and electrical leakage may occur. Furthermore, since the neon tube and the fluorescent tube are made of glass tube, these have drawback in their impact resistance, so the neon tube and the fluorescent tube can not be used at such a place that an object including a person or a vehicle may come in contact with the tube.
Another conventional light transmitting tube is formed by filling a transparent core liquid or flexible transparent polymer into a flexible tube. A further another light transmitting tube is prepared by twisting plastic optical fibers. Light generated from a light source is entered into each of the tubes through an end of the tube and emitted out of the surface of the tube over a length of dozens of meters so that the light source and the emitting portion are separately provided, thus reducing the danger of damage. Therefore, the light transmitting tube can be used in water, outdoors, or an environment having a possibility of explosion. In addition, since complex process including glass blowing is not required, the light transmitting tube can be easily manufactured and can provide good workability.
Conventionally, in the light transmitting tube having a liquid core, when bent as shown in FIG. 3, many light beams have angles of incidence relative to the outer surface of the tube, which are smaller than the critical angle, at the bent portion, thus increasing the optical leakage (optical loss) out of the core. This has been a problem. Therefore, materials have been selected to increase the difference between the respective reflective indexes and many structural designs have been made to reduce the optical loss at the bent portion as much as possible. However, it is difficult to select such materials because of requirement of transparency and it is also difficult to design structure for each of applications.